1. Field of the Invention
The present invention generally relates to plasma control in a semiconductor substrate processing system and, more particularly, to plasma control using a dual cathode frequency mixing technique.
2. Description of the Related Art
The increase in size of plasma enhanced semiconductor processing chambers contributes to a spatially variant effect over the surface of the substrate being processed. That is, as the size of the substrate being processed approaches the wavelength of the frequency that is used to bias the substrate, a spatial variation in the RF power distribution forms over the surface of the substrate (e.g., proximate the cathode that forms an electrode). This spatial variation can be frequency dependent in the regime of higher frequencies (shorter wavelengths), larger substrates, or combinations of the two. This spatially variant effect has a negative impact on process uniformity. For example, in an etch reactor, the standing wave effect can cause non-uniformity in the etched substrate surface.
Therefore, there is a need for an improved method and apparatus for semiconductor substrate processing that combats this spatially variant effect.